The use of copper (Cu) metal in multilayer metallization schemes for manufacturing integrated circuits requires the use of a diffusion barrier layer to promote adhesion and growth of the Cu layers and to prevent diffusion of Cu into the dielectric materials. Barrier layers that are deposited onto dielectric materials can include refractive materials, such as tungsten (W), molybdenum (Mo), and tantalum (Ta or TaN), that are non-reactive and immiscible in Cu, and can offer low electrical resistivity.
More recently, ruthenium (Ru) metal has been identified as a potential barrier layer for copper metallization since it is expected to behave similarly to the above-mentioned refractory metals. Furthermore, it is possible that a single Ru layer can replace current barrier layers, including TaN/Ta bilayers. In addition, recent research has suggested that a bulk Cu deposition can be performed by direct Cu plating onto a Ru layer without depositing a Cu seed layer onto the Ru layer. However, the as-deposited Ru layer may contain contaminants, for example due to by-products from the Ru deposition process that may become incorporated into the Ru layer, that can result in unacceptable properties for the Ru layer when it is integrated into Cu metallization schemes. These properties include insufficient resistance to Cu diffusion through the Ru layer, poor Cu plating uniformity over the whole substrate (e.g., 200 mm, 300 mm, or even larger wafers) that subsequently can lead to problems during planarization of the substrate by chemical mechanical polishing (CMP), weak adhesion between the bulk Cu layer and the Ru layer that can result in electro-migration (EM) and stress-migration (SM) problems, as well as reduced device production yields. Thus, new processing methods are needed for improving the properties and integration of Ru layers into Cu metallization schemes.